Superabsorbents, that is to say absorbent material which is capable of absorbing several times, normally more than ten times, its own weight of water or body fluid, is used in absorbent articles, such as diapers, incontinence guards sanitary napkins, to enhance the absorbency of the absorbent body of the article and also retention capacity, the remainder of the absorbent body normally consisting of cellulose fibres so-called fluff pulp.
Polyacrylic acid is the polymer most used as superabsorbent non-renewable base. Polyacrylic acid is produced from oil. Since crude oil is a natural resource that is non-renewable, the use of oil as a starting material in the manufacture of polyacrylic acid creates a problem from an environmental aspect.
With the intention of resolving this problem, endeavors have been made to produce superabsorbents on the basis of renewable primary materials. These primary materials have included the different polysaccharides, such as starch and cellulose. One polymer that has been used to a great extend in this context is carboxymethyl cellulose. This is a cellulose derivative with carboxymethyl as a subsistent. The properties of the polymer are contingent on the degree of polymerization, DP, and the degree of substitution, DS. Carboxymethyl cellulose is relatively cheap and hu high affinity to water-based liquids.
However, the admixture of carboxymethyl cellulose in absorbent articles such as diapers, incontinence guards and sanitary napkins is associated with serious drawbacks. When the article is wetted tiring use, the carboxymethyl cellulose will dissolve and therewith increase the viscosity of the liquid discharged by the wearer. This dramatically reduces the liquid dispersion rate. So-called gel blocking occurs. Carboxymethyl cellulose that has a degree of substitution below 0.35 is not soluble in water and could therefore be used favorably in absorbent articles with regard to the aspect of gel blocking. However, carboxymethyl cellulose that has a degree of substitution below 0.35 has pour absorption properties in comparison with polyacrylates. In other words, the carboxymethyl cellulose must have a degree of substitution greater than 0.35 in order to hive good absorption properties, although such carboxymethyl cellulose is soluble in water and therewith presents a gel blocking problem.
Another drawback with the superabsorbents that are commercially available at present is the administration foam. The superabsorbent is normally added to the article in which it shall be included in the form of grains, flakes or granules. A special metering apparatus is required to add superabsorbent in this form, and it is difficult to obtain uniform distribution on of superabsorbent in the fibrous pulp body.
Superabsorbent in fibre form would be easier to meter. Because the absorbent body into which the superabsorbent is to be administered normally consists of fibres, there is a danger of superabsorbent particles separating-out from the fibre matrix. This problem is alleviated with superabsorbents in fibre form. Although polyacrylate fibres are commercially available, they have not been used to any great extent. This is probably due to their high price and poor swellability.
A number of attempts have been made to produce polysaccharide fibres for use in sanitary products. WO 93/12275 discloses solvent spinning of polysaccharide fibre. However, the swelling properties of polysaccharide fires produced in accordance with known techniques is too poor for such fibres to be of interest as a substitute for conventional superabsorbent material.